If you're camping or just too broke for the laundromat you can make a dirt cheap washing machine using a large bucket and a standard bathroom toilet plunger.
Bucket re-purposing weblog Five Gallon Ideas shares an easy method to build a DIY washing machine. Using a large bucket with a tight fitting lid, drill a small hole in the lid just large enough for the handle of your plunger to move through. Then drill around a dozen 6.35mm holes on the sides and top of the plunger to allow the water and soap to flow through properly. To use you'll just need to fill the bucket halfway with water, add your soap and dirty clothes and pump the plunger up and down for several minutes.
If you'll be travelling you can also skip the plunger and drill and just wash clothes in your car using a large bucket.
Washing Machine [Five-Gallon Ideas]